The origin of the foundation of Lefkada’s emblematic castle dates back to the dawn of the 14th century, when the Latin ruler of the island, Giovanni Orsini, built a small fortress at the northeastern end of the islet situated between Lefkada and Acarnania, at the site of Gyra, in order to secure the island from enemy raids. The original fortress probably had a rectangular plan and was reinforced with high four-sided towers at its corners. Unfortunately, the remains of this original fortification are no longer visible today, making any conclusions as to the original form of the fort difficult and risky.
The castle remained under the control of the House of Orsini until 1331 when Walter or Gautier VI de Brienne, Count of Brienne and of Lecce, seized Lefkada and the castle of Agia Mavra. The deposed Duke of Athens led a “crusade” to reclaim Athens from the Catalans, supported by the Pope and the Angevin kings of Naples.
The price for this support was initially to detach territories from the Despotate of Epirus. As part of this campaign, he attacked the vulnerable castle of Lefkada with a force of 800 knights in armor, and thus the capture was achieved relatively easily. The subsequent year, however, the crusade came to an inglorious end and Walter returned to Italy. The Angevins, nonetheless, remained on the island without making any changes to the small castle.
In 1355, Walter ceded dominion over the island to his confidant, Graziano Zorgi from Venice. By then, Agia Mavra had already evolved into a feudal castle, where the feudal lord resided with his family, alongside the Catholic bishop with his entourage, as well as certain officials and the garrison.